Allison 5sp: LML piston difference

[ikeG]

Noticed that a new replacement acdelco piston is not bank specific whereas the original ones in this 2012 are. Ordered using the vin & everything. Anyone run into this?

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[Chevy1925]

im not really surprised. its only .030 different off set from center. all the aftermarket are centered as well.

something doesnt seem right though. making the oil squirter holes different depths but then clearancing each side for the squirter doesnt make sense nor would you put a front or back arrow, you would only need an indicator for "TOP" for oil squirter orientation.

did you measure to see what the off set difference between the old and new piston had in teh wrist pin area? maybe this was a screw up?

 

[ikeG]

im not really surprised. its only .030 different off set from center. all the aftermarket are centered as well.

something doesnt seem right though. making the oil squirter holes different depths but then clearancing each side for the squirter doesnt make sense nor would you put a front or back arrow, you would only need an indicator for "TOP" for oil squirter orientation.

did you measure to see what the off set difference between the old and new piston had in teh wrist pin area? maybe this was a screw up?

I jumped the gun on posting. I edited bunch out on OP. Let me figure it out and I'll update

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[ikeG]

Pin offset is same as OE. Goofy thing is the oil hole is really far away from the nozzle now.

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[ikeG]

And this hole is on the opposite side of the pin too.

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[ikeG]

I double checked the part numbers 3 times at 2 different dealers. Tried a vin from a different year lml too. I even ordered a 2nd piston and its identical. It's also the same part number that vendors list for OE replacement

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[Chevy1925]

hmm that is strange. wonder if they went chinese mfg and they missed that part...

 

[ikeG]

It seems like they made them ambidextrous on purpose but the arrow should have been left off. It will only face forward on the left bank. Am I thinking right??

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[Chevy1925]

It seems like they made them ambidextrous on purpose but the arrow should have been left off. It will only face forward on the left bank. Am I thinking right??

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well if pin off set is the same on both, that would mean they will be side specific as the off set will be .060 the wrong way if on the wrong side. if its centered like you originally though, it can be used on either side. it was the pin off set that made them side specific originally. the squirter holes just followed suit to the side the piston was made for.

 

[ikeG]

With nozzle relief on both sides, you can spin the piston to use on either side. Right? .030" offset in or out, just spin it around.

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[Chevy1925]

With nozzle relief on both sides, you can spin the piston to use on either side. Right? .030" offset in or out, just spin it around.

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Accept for like you pointed out that one side is recessed much more than the other. Which is where the arrow plays apart again. Does the nozzle hit the piston if you flip it correctly or can the nozzle recess into the hole more without issue? I’d rather have it go in more (more oil getting inside the piston to cool) than the other way round

 

[ikeG]

Accept for like you pointed out that one side is recessed much more than the other. Which is where the arrow plays apart again. Does the nozzle hit the piston if you flip it correctly or can the nozzle recess into the hole more without issue? I’d rather have it go in more (more oil getting inside the piston to cool) than the other way round

I guess I was confusing on that part. The oil hole in the new piston is the same depth on either side. Which means the nozzle tip stays a good amount away from the hole in either bank.
The nozzle clears either way. I've installed it both ways now to verify.
The new piston has the pin offset but also has matching oil nozzle reliefs and holes on both sides. Which makes it ambidextrous. But yet they still put the arrow on the top.

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[Chevy1925]

I guess I was confusing on that part. The oil hole in the new piston is the same depth on either side. Which means the nozzle tip stays a good amount away from the hole in either bank.
The nozzle clears either way. I've installed it both ways now to verify.
The new piston has the pin offset but also has matching oil nozzle reliefs and holes on both sides. Which makes it ambidextrous. But yet they still put the arrow on the top.

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Ooohhh! That is interesting! Are they numbered like the 01-10 pistons were?

 

[Fingers]

The offset is supposed to be relative to crank rotation. Is there any mark on the top of the pistons?

 

[ikeG]

Piston top.

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[ikeG]

Piston says made in Mexico.

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[Fingers]

Arrow points to the front of the engine. Since the oil holes and squirter reliefs are ambidextrous, the offset will be in the correct direction in either bank so long as the arrow points forward.

 

[ikeG]

Thanks Jon.

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